Rather than making entire electronic systems that are designed to perform a particular function, manufactures of networking equipment and other electronic systems have realized that they may manufacture a modular chassis that holds replaceable cards with varying functionalities. Accordingly, each customer can purchase and fill their modular chassis with cards that have the required functionality to meet their particular desires. Modular chassis and their associated cards allow customers flexibility, the ability to easily expand capability, the ability to easily switch functionality, and a number of other benefits.
The theory behind the modular chassis is that most cards have the same overall requirements with respect to power and other essentials provided by the chassis. Therefore, numerous cards may be designed in the same form factor and with the same chassis interface. Cards that are designed in such a manner are interchangeable within a chassis.
The problem is, that in reality, many cards have different needs in terms of size and power requirements. The diverse requirements of different line cards makes it practically impossible to design a system with a card form factor optimized for all cards, card sizes and card power requirements. Accordingly, cards are made in different form factors and multiple chassis are needed. One solution is to have one system optimized for small cards with low power consumption and another system optimized for large cards with high power consumption. This solution has many disadvantages. For example, customers often need a mixture of small and large cards, which requires them to buy both a small and large chassis. Moreover, customers' systems often grow as they mature and this growth may require a different mixture of cards not supported by the current chassis. Having to upgrade an entire chassis to support a new card form factor is extremely expensive for the customer.
Another solution is to have a card adapter for small cards that allows the card with the smaller form factor to plug into a slot designed for a large card. One problem with this solution is that it wastes considerable chassis space because a small form factor card takes up an entire large form factor slot.